The present invention relates to air bag tethers and to a pattern-wise arrangement of such tethers in relation to air bag panels on a fabric blank, thus resulting in increased fabric utilization and an overall cost savings per finished air bag. The air bag tether system of the present invention is comprised of two congruent tether panels that are joined to one another and to a respective air bag panel. In a preferred embodiment, the tether panel that is attached to the face panel of the air bag is cut in alignment with the warp and the fill of the fabric blank, while the rear tether panel (which is attached to the rear panel of the air bag) is cut on the bias with respect to the warp and the fill of the fabric blank. This two-piece construction, with one bias-cut piece, decreases the amount of fabric that is used in the manufacture of the air bag and tethers, while providing sufficient elongation for the tether system to be functional.
Traditionally, air bag tethers have been used to control the excursion of an air bag as it inflates. As gas is released, causing the air bag to rapidly inflate, it is necessary to keep such inflation from occurring in an uncontrolled manner. Tethers, which are sewn to the face and rear panels of an air bag, keep the inflating air bag from expanding so rapidly as to adversely affect the safety of the vehicle occupant, as the vehicle occupant contacts the air bag.
Tethers are conventionally strip-shaped pieces of fabric that are aligned in pattern-wise arrangement on a fabric blank, or are aligned in relation to air bag panels that may be cut from the same blank. The patterns for these tethers may include a circular portion in the center area of the tether strip around which the strip is attached to the air bag panel. It is understood that such tethers should have a capacity for elongation (that is, the tethers should be able to stretch to accommodate the rapid excursion of the bag). For this reason, conventional tethers have been cut on the bias with respect to the warp and fill of the fabric. However, aligning the tether patterns to fulfill this condition increases the amount of fabric needed to create an appropriate number of tethers for a plurality of air bags. Furthermore, because fabric utilization comprises more than fifty percent of the costs of a finished air bag, aligning the tethers in this manner increases production costs.
The present invention addresses the problems of fabric utilization and tether elongation. By understanding that the portions of the tether that are connected to the rear panel typically J experience a greater level of stretch than the tether portions connected to the face panel, a fabric-saving solution was created. Instead of the entire tether length being cut on the bias, only that portion of the tether attached to the rear panel is cut on the bias. Using a two-piece tether system in which only the rear tether panel is cut on the bias increases fabric utilization by allowing these bias-cut tether portions to be arranged around air bag panels into spaces which otherwise would be considered fabric waste. The portion of the tether that is attached to the face panel is cut in alignment with the warp and fill of the fabric. The combination of the bias-cut and alignment-cut tether portions leads to an improved fabric utilization, while providing a tether system that is capable of sustaining the forces exerted by the inflating air bag.